In Windows DLL builds we inject operator new/delete definitions into
classes with a leak detector. This requires that all inheritance from
such classes must be public, and classes inheriting from multiple such
classes must disambiguate between the base's operators.

MIDI only plugins are no longer provided valid audio buffers
Graph nodes are only executed when they have active connections

When plugins change their 'parameter info' this often means that their
previous parameter text is no longer valid, so we should fetch new text
to represent the parameter value.

This change was primarily tested with Kontakt.

Adds a mechanism to notify the host that the plugin state needs saving,
using updateHostDisplay.

Also allows JUCE hosts to detect when a plugin needs its state saving
via the AudioProcessorListener.

This commit removes the various compiler-specific JUCE_DEPRECATED macros and replaces them with C++14's deprecated attribute. It also removes the JUCE_CATCH_DEPRECATED_CODE_MISUSE flag as we can rely on the override specifier catching usage of these old virtual methods, and tidies up the DOXYGEN preprocessor checks as they were inconsistent across the codebase.